1. Field of the Invention
The invention is directed to a drive unit for a motor vehicle including an electric machine, a clutch and a release member which is axially displaceable by an actuating device arranged at least partially in a space surrounded by the stator of the electric machine.
2. Description of the Related Art
A generic drive unit of the kind mentioned above has been known, for example, from U.S. Pat. No. 8,267,208 and can be used by itself or in combination with an internal combustion engine in the drivetrain of a motor vehicle. The clutch which is constructed to form a constructional unit with an electric machine can couple or uncouple the rotor of the electric machine to or from a further drive element of the vehicle drivetrain, in this case particularly an internal combustion engine, depending on operating state, by an actuating device arranged inside the stator. The actuating device is preferably provided in this case as a hydraulically or pneumatically working central clutch controller.
This constructional unit has been found to be disadvantageous in that the installation expenditure incurred by installing the pressure transmission lines of the clutch actuation device is relatively high and the installation space requirement is correspondingly large. Further, the gear ratios of the actuation device can vary as a result of the required long pressure lines and the temperature dependency of the fluid used and can therefore adversely affect a desired magnitude of the release stroke of the clutch.
EP 0 716 242 B1 discloses an actuating device which does not belong to the generic type mentioned above and which has an electric motor drive for a vehicle friction clutch that can be actuated by a diaphragm spring. The electric motor drive has an electric actuator drive motor with an actuator drive shaft which is directed transverse to a release axis of the clutch and which engages by means of a worm in an externally toothed housing segment of a release bearing of the clutch, this housing segment forming the worm gear. The release bearing housing is rotatably arranged at a stationary holder by means of a quick thread. During rotational movement of the actuator drive shaft, the bearing housing executes a rotational movement which undergoes a simple reduction by the worm-worm gear combination and which is simultaneously converted into an axial movement owing to the quick thread. In this way, a release bearing arranged at the end of the housing is moved toward a clutch release member causing the clutch to be released.
In this actuating device, the quick thread requires a relatively high actuating torque to displace the release bearing housing, for which reason the selected radial distance of the worm drive from the rotational axis or release axis must be relatively large. Further, the actuator drive shaft of the electric machine which is fastened to the outer side of an approximately cylindrical gear unit housing must be dimensioned so as to have sufficiently great bending strength and torsional strength. In other respects, the axial width of the worm gear segment must be selected such that an engagement with the worm is ensured over the entire actuating path during an actuating process. Since, in addition to a rotational movement, the worm gear segment is axially displaced against the action of the diaphragm spring, very high friction forces occur at the worm gear unit which adversely affect the efficiency of the actuating device.
Proceeding from the prior art cited above, it is an object of the invention to improve a generic drive unit particularly with respect to the actuating device of the clutch.